Crocodylomorph Trackways from the Jurassic to Early Cretaceous of North America and Europe: Implications for Ichnotaxonomy

Trackways described as Batrachopus (Batrachopodidae Lull, 1904 Lull, R. S. 1904. Fossil footprints of the Jura-Trias of North America. Memoirs of the Boston Society of Natural History, 5: 461–557.  Google Scholar]) from the Lower Jurassic of Europe are rare and in some cases different from the type trackways from North America. Differences may be in part attributable to preservation, but current evidence suggests that there is inherent variability in Batrachopodidae morphotypes, beyond that attributable to differential preservation. Type Batrachopus is a stout-toed form, with minimal digit divarication (i.e., a long foot), whereas Antipus describes slender-toed forms with a wider foot and wider digit divarications.

Antipus is also similar to Crocodylopodus (ichnofamily Crocodylopodidae: Fuentes Vidarte and Meijide Calvo, 1999 Fuentes Vidarte, C. and Meijide Calvo, M. 1999. Primeras Huellas de Cocodrilo en el Weald de Cameros (Sria, Espana) Nueva Familia Crocodilopodidae: Nuevo icnogenero: Crocodylopodus Nueva icnoespecie: C. meijidei. Actas de las jornadas internacionales sobre paleontologia de dinosairios y su entorno. Sala de los infantes (Burgos, Espana). Collectivo Arqueologico-Paleontologico de Salas, : 329–338.  Google Scholar]) from near the Jurassic-Cretaceous boundary in Spain. Crocodylopodus has a relatively large manus, and a less outwardly rotated trackway, but is not sufficiently different from Batrachopodidae to warrant its own ichnofamily. Manus-pes size (area) ratios (heteropody) may also be important in differentiating different crocodylomorph ichnotaxa, as is the case with other archosaurian ichnotaxa. However, heteropody may change with size, and be less pronounced in large individuals. Manus and pes rotation patterns, and trackway width are variable and may be of use for differentiation of ichnotaxa but may also be a function of speed.